1. Field of the Invention
This invention relates to a material for a casing for an acoustic equipment and the casing for the acoustic equipment. More particularly, it relates to a material for a casing for an acoustic equipment containing a cellulose-based powdered material and the casing for the acoustic equipment.
2. Description of Related Art
In an acoustic equipment represented by television, stereo system, radio cassette recorder or headphone, developments for improving its sound quality are proceeding. In particular, it is desired to improve an output sound pressure, distortion factor or flatness, among acoustic properties for acoustic equipments, such as a speaker or a headphone system.
In the above-described acoustic equipments, various physical properties of the acoustic equipments, such as a speaker box or a housing for a headphone system, are thought to be crucial as factors influencing the above-mentioned acoustic properties. If the sound wave is produced as a result of actuation of the acoustic equipments, the casing thereof undergoes resonant vibrations due to the produced sound wave. The audible sound outputted by the acoustic equipments is deteriorated in sound quality due to the resonant vibrations.
For overcoming these inconveniences, it may be contemplated to use a material of high tenacity having a moderately large internal loss in the casing for the acoustic equipment for improving an output sound pressure, distortion factor or flatness. Wooden plates, such as lauan plates, or particle boards, obtained on coating an adhesive on fine wooden chips for forming into a plate, have been used to this purpose.
However, these plate materials, formed into plates, are limited in degree of freedom as to the outer shape, and hence are limited in usage. Since the process of assembling the plate materials formed into a desired shape, is required, productivity is necessarily lowered.
For overcoming these difficulties, there is known a casing for an acoustic equipment fabricated by injection molding a thermoplastic resin. The materials used for forming a casing for an acoustic equipment may be enumerated by composite materials obtained on mixing an inorganic filler to polypropylene (PP) and a general-purpose plastic materials, such as ABS resins. The inorganic fillers mean powders formed of mica, talc and calcium carbonate and so forth.
The casing for an acoustic equipment is increased in tenacity as a casing by the inorganic fillers. However, if the inorganic fillers are used, the internal loss is increased such that the casing is inferior to the above-mentioned wooden casing as to the output sound quality of the equipment. If the ABS resin is used in place of PP, resonant vibrations are produced in the casing of the acoustic equipment because of the small internal loss, thus generating distortion in the output sound of the equipment. Thus, the casing cannot be said to be optimum as the casing for the acoustic equipment.
Meanwhile, if the casing for the acoustic equipment is formed of wood, the output sound produced is of good sound quality. As the material for the casing of the acoustic equipment, a mixture of cellulose-based fillers, such as wooden powders or husks of grains, with a resin, is used for producing the sound quality comparable to that obtained with the use of a wooden material. The cellulose-based fillers are surface-processed, such as with phenol, for improving dispersion with respect to resin. However, as compared to the above-mentioned generic inorganic fillers, the cellulose-based fillers cannot be said to have sufficient lubricating properties. Thus, the amount of the cellulose-based fillers that can be added to the resin is limited, with the result that the material of the casing for the acoustic material cannot be improved in tenacity.
If a speaker is driven with a signal of a pre-set level, the casing of the acoustic equipment containing the cellulose-based filler undergoes resonant vibrations by vibrations imparted to the speaker. The result is that playback sound pressure frequency characteristics of the speaker is not stable but undergoes fluctuations. This is not desirable because the distortion is increased by resonant vibrations of the casing for the acoustic equipments.
With the casing for the acoustic equipments employing the cellulose-based fillers, the surface of the casing becomes fluffy because the cellulose-based fillers are of a fibrous structure. The result is that not only the casing is unsatisfactory in appearance but also the speaker cannot be said to be optimum in output sound quality.
In a casing for an acoustic equipment, employing the cellulose-based fillers, only resins with lower melting temperatures, such as PP or vinyl chloride (PVC), can be used because the cellulose-based filler is poor in thermal resistance. That is, the casing for the acoustic equipment has a drawback that the usable resin type is limited.
When the cellulose-based filler is mixed and molded with the resin, lignin or pyroligneous acid is produced, as a result of which the casing containing the cellulose-based filler undergoes corrosion.
It is therefore an object of the present invention to provide a material for a casing for an acoustic equipment which resolves the above-mentioned problems.
It is another object of the present invention to provide a casing for an acoustic equipment which resolves the above-mentioned problems.
In one aspect, the present invention provides a material for a casing of an acoustic equipment mainly composed of a filler and a thermosetting resin, wherein the filler is comprised of a cellulose-based powdered material on the surface of which is immobilized a powdered material harder and smaller in particle size than the cellulose-based powdered material.
In another aspect, the present invention provides a material for a casing of an acoustic equipment mainly composed of a filler and a thermoplastic resin, wherein the filler is comprised of a cellulose-based powdered material on the surface of which is immobilized a powdered material harder and smaller in particle size than the powdered material.
In still another aspect, the present invention provides a casing of an acoustic equipment obtained on molding a starting material mainly composed of a filler and a thermosetting resin, wherein the filler is comprised of a cellulose-based powdered material on the surface of which a powdered material harder and smaller in particle size than the cellulose-based powdered material is deposited under a pre-set pressure.
In yet another aspect, the present invention provides a casing of an acoustic equipment obtained on molding a starting material mainly composed of a filler and a thermoplastic resin, wherein the filler is comprised a cellulose-based powdered material on the surface of which a powdered material harder and smaller in particle size than the cellulose-based powdered material has been deposited under a pre-set pressure.